The go-pp library —"pp" being for "pretty printer"— contains utilities to pretty print Go values. Its main use case is to help debugging. The %#v standard formatting sequence is fundamentally user hostile: no indentation, prints pointers instead of recursing, expands values that should not be expanded (e.g. time.Time values).

The printing algorithm tries its best to present values in a useful way. Types are printed when it makes sense, simple values are displayed inline when possible, various standard types have a custom representation.

Example:

info, _ := os.Stat("/dev/stdout")
p.Print(info, "standard output")

Debugging is hard. The pp package makes it easier.

Import go.n16f.net/pp and call pp.Print with any value as argument. Extra arguments are used as a format string and arguments to add a label to the output.

For example:

pp.Print(os.Getenv("HOME"), "home directory")

[command line arguments] []string(["./test"])

Printers can be configured with various settings to match your preferences. The following options are available:

• (*Printer).SetDefaultOutput: set the output (io.Writer) used by the printer for the Print method (default: os.Stdout).
• (*Printer).SetFormatValueFunc: set the function used to override value formatting. See the section about custom formatting below for more information (default: pp.FormatValue)
• (*Printer).SetMaxInlineColumn: set the column beyond which the printer will revert to the normal output format when trying to print a value inline (default: 80).
• (*Printer).SetIndent: set the string used for each indentation level (default: " ").
• (*Printer).SetLinePrefix: set a string to be printed at the beginning of each output line.
• (*Printer).SetPrintTypes: control type printing. Can be either:
  • pp.PrintTypesDefault: print the type of values when it is not obvious;
  • pp.PrintTypesAlways: print the type of all values;
  • pp.PrintTypesNever: never print any type.
• (*Printer).SetHidePrivateFields: hide private (non-exported) fields when printing structures.
• (*Printer).SetThousandsGroupingMinDigits: the minimum number of digits for a number to be printed with thousand separators (default: 6).
• (*Printer).SetThousandsSeparator: set the character (rune) used between groups of three digits when printing numbers (default: '_').

You can either modify the default printer used by pp.Print (pp.DefaultPrinter) or create your own printer.

See the custom-printer program for an example.

Printers are thread safe.

It is possible to control the representation of specific types. Use (*Printer).SetFormatValueFunc to pass your own function.

The function accept a reflect.Value argument and can return an any value which can be either:

• nil to use the default printer representation;
• a value of type RawString to print the value as a string without any further formatting (e.g. RawString("foo") will simply print foo);
• any other value to be formatted by the printer.

Printers will only call this function on values, not pointers.

The default function, pp.FormatValue handles various standard types such as time.Time or regexp.Regexp.

See the custom-formatting program for an example.

Refer to the Go package documentation for information about the API.

Go-pp is open source software distributed under the ISC license.